Hysteresis drive for high speed print hammers



Nav. 11; k1969 A, NYMAN l f 3,477,365

HYSTERESIS DRIVE FOR HIGH SPEED PRINT HAMMRS Filed July 22, 1966 A 2 sheets-sheet i E v .w/,l .f

-r A l -dh INVENTOR' ALEXANDER N'YMAN ATTORNEY Nw.` A11, 1969 A. NYMAN HYSTERESIS DRIVE FOR HIGH SPEED PRINT HAMMERS v Filed July 22,5 1966 25 Fig.4 S 24 CURE ENT 2 Sheets-Sheet 2 Figb.

United `States Patent Of 3,477,365 HYSTERESIS DRIVE FOR HIGH SPEED PRINT HAMMERS Alexander Nyman, Dover, Mass., assiguor, by mesne assignments, to Mohawk Data Sciences Corporation, East Herkimer, N.Y., a corporation of New York Filed July 22, 1966, Ser. No. 567,307

Int. Cl. B41j 9/38 U.S. Cl. 101-93 13 Claims ABSTRACT OF THE DISCLOSURE This invention applies to high speed printing and particularly to printers in which rapidly moving fonts of selected characters pass print locations and high speed hammers are actuated when the required characters in the font are in position for printing. Energy in a rotating ferromagnetic drum is transferred to the hammers when hysteresis and eddy current drag is induced in the drum by activating elements that are connected to the hammers.

It has been found that for printing rates in excess of 20 lines per second, print hammer speeds in excess of 100 in./sec. are desirable. Increasing hammer speeds decreases the required hammer mass by an inverse square function. For example, doubling the speed permits the use of print hammers with JA of the mass. It has been found also that the clarity of printing at high speeds depends largely on the duration of the penetration period-the time taken by the hammer to enter into the printing medium and to retract from it. This duratiion is reduced by decreasing the hammer mass which can be accomplished without reducing the kinetic energy by increasing the velocity of the print hammer.

In the present invention, a printing hammer or pellet is driven at a high velocity by the use of the force developed by hysteresis and eddy currents from a ferromagnetic drum spinning at a high speed adjacent to the hammer or pellet. T-he energy transfer takes place when an activating element attached to the hammer is magnetized in such a Way as to permit the required hysteresis and eddy current drage to be induced in the drum. The variations in magnetism are accompanied with dissipation of energy which produces a driving force on the hammer in the direction of movement of the surface of the spinning drum. The printing hammer can also be controlled during the penetration period and the rebound period by controlled magnetization of the hammer activating elements.

It is thus an object of my invention to utilize the energy transfer forces due to hysteresis and eddy currents to provide kinetic energy to a ballistic object.

A further object is to derive the hysteresis and eddy current energy from a rapidly rotating mass to develop kinetic energy in a ballistic object when the object is magnetically energized.

A further object is to provide a compact mechanism utilizing hysteresis forces to drive an array of print ham? mers for use in high speed printers.

A further object is to control the forces applied to hammers during their activation period, penetration period and rebound period.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a perspective view of a first embodiment of the invention.

Patented Nov. 11, 1969 FIG. 2 is a cut-away view illustrating in detail a portion of the first embodiment of the invention.

FIG. 3 is a perspective view of a second and preferred embodiment of the invention.

FIG. 4 is a cut-away View of an element of the preferred embodiment of the invention.

FIGS. 5a and 5b` are timing diagrams showing the operatio'n of the preferred embodiment of the invention.

As shown in FIGS. 1 and 2, a group of printing hammers 1 are arranged along a row. These hammers cooperate with a print drum or chain of type to effect printingVH on a document according to well-known techniques. Printing is accomplished -by selectively driving the hammers in the upward direction when the appropriate type faces are in position for printing.

Each hammer 1 is formed at the end of a magnetizable shaft 3 which is mounted in position for vertical movement by two flexible reeds 5. Alternate hammers are mounted to one side of a ferromagnetic frame 7 while the interspersed hammers are mounted to the other side of the frame. This alternate arrangement is not essential, but is `preferred because it simplifies the assembly of components by providing greater space between adjacent components. Two ferromagnetic iluted drums 9 are continuously rotated on mounting shafts 8 with opposite directions of revolution between shoe portions 10 of the shafts 3 and the frame 7 such that the surfaces of both drums move past the shafts in the upward direction. A magnetizing coil 11 is rigidly mounted on the frame 7 to surround a corresponding shaft 3.

`Hammer operation is effected by passing current through the coils 11 at the appropriate times to cause the corresponding shafts to be magnetized. The magnetic fields that are thus developed are passed through the shafts 3, drums 9 and frame 7.

Due to hysteresis and eddy current in the drum 9 as it rotates in the magnetic field emanating from the shaft 3, a magnetic force is developed by the drum. The upwardlymoving field exerts an upward force on the shaft as long as the shaft is magnetized. The current pulses to coils 11 are of short duration, magnetizing the shafts 3 long enough to impart vertical upward velocity to the hammers. T-he pulse current is interrupted prior to printing impact time so that after printing the hammer head and shaft travel freely downward with some damping caused by the relaxing magnetic field. A damper 13 is located beneath each shaft 3 to absorb the remaining rebound energy. The operation of the hammers can also be controlled during the penetration period and the rebound period by applying current` to the coils 11, as will be described in greater detail with respect to embodiment shown in FIG. 3.

Many components are exaggerated in size in the draw ings for the sake of simplicity. In practice, a velocity of about in./sec. is obtained for a hammer 1 and shaft 3 weighing in the order of .002l lb. with a flight time of about 1.4 milliseconds and an average acceleration in the order of 100,000 in./sec.2 (260G). Therefore, the upward drag force from the drum is about 260 .002=.54 lb. Thus, with a strong magnetic field (eg. 20,000 gauss or more), this force is obtained with an extremely small area (less than .01 sq. in.) of the shaft in the Vicinity of the drums.

While uted drums are preferable to reduce the interaction between elements, plain drums are suitable for use. Furthermore, a single drum can operate all hammers while retaining the alternating mounting of adjacent hammers by aligning all shafts. Similarly, two drums can be used with both drums adjacent to all shafts to increase the forces developed in the shafts.

FIG. 3 shows a preferred embodiment of the invention. The hammers 1 are mounted on shafts 3 and are suspended by reeds 5 in the same manner as shown in FIGS. 1 and 2. Similarly, a damper 13 is arranged below the shaft. However, the shafts 3 in the preferred embodiment need not be magnetic as they support magnetic armatures 20 which move with the shafts. As shown in detail in FIG. 4, the armature 20 contains four pole-face areas 21, 22, 23, and 24 and a coil 25. The areas 21 and 22 are adjacent to the left drum while areas 23 and 24 are adjacent to the right drum. In contrast to the embodiment of FIGS. 1 and 2, in FIG. 3, the drums are rotated with the same direction of revolution and by themselves would not be effective to operate the hammers because opposing hysteresis drags would be developed. However, the drums are also magnetized as shown by permanent magnets 26 with extended pole pieces 27. While ceramic magnets are more effective, metallic magnets can be used.

The combined effects of the two magnets is to balance their drag on the armature 20 except when current is passed through the coil 25. When the current is in such a direction as to make north poles 21 and 23 and south poles 22 and 24, then poles 21 and 22 react with left drum 9 (left side) to cause an upward drag force on the armature 20. At the same time the polarity of poles 23 and 24 rejects the magnetic field from the right drum abolishing its downward drag. The hammer 1 is thereby driven u ward to effect printing.

To speed up rebound time, the current in coil 25 is reversed at or near the instant of printing. This causes the poles 23 and 24 to cooperate with the magnetization of the right drum to cause a downward drag on the armature.

In order to avoid excessive downward speed, this reversed pulse can be reversed again to stabilize the armature when it reaches its rest position. FIG. 5a illustrates the control of the current in coil 25. When the hammer is to be actuated, a pulse 31 of current is applied. This pulse provides upward acceleration of the hammer as shown on the corresponding portion of the travel/time chart in FIG. 5b. After the printing impact at time T, and without the use of damping currents, the hammer head would rebound as shown by the dashed line in FIG. 5b, and eventually reach stability in some to 15 milliseconds with some bouncing on the damper 13. However, by applying pulses such as 33 and 35, the hammer head is first driven downward at high speed by pulse 33 and then decelerated by pulse 35. Electronic circuits capable of achieving such a sequence of pulses are well known in the art and are not a part of this invention. The rapid withdrawal and stabilization of the hammer is of great importance for high speed printing. By this means the same hammer can be reactuated in a very short time, accelerating the performance of the printer.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A hysteresis drive comprising, in combination:

a rotating magnetizable driving element;

a selectively magnetizable driven element located adjacent to the driving element and mounted for movement with respect thereto;

means for magnetizing the driven element; and

means .for directing at least a portion of the magnetic flux generated by said magnetizing means through said driving element, the rotation of the latter exerting, through hysteresis drag, a driving force on said driven element.

2. The device described in claim 1, wherein the magnetizing means is electromagnetic.

3. The device described in claim 2, further comprising means for controlling the current in the electromagnetic magnetzing means to cause resulting forces on the driveri element which are successively in opposite directions.

4. A hysteresis hammer drive comprising, in combination:

a plurality of hammers aligned in a row and each adapted for substantially linear movement in the same direction;

a plurality of hammer shafts, each mounted to a hammer, each extending in said directions of movement, and each comprising a magnetizable element;

a rotating magnetizable drum having its axis parallel to the row of hammers and arranged closely and tangentially to the magnetizable elements of the hammer shafts;

electromagnetic means for selectively magnetizing one or more of said magnetizable elements; and

means for directing at least a portion of the magnetic flux generated in said one or more magnetized elements through said drum, the rotation of the latter exerting, through hysteresis drag, a driving force on said one or more elements.

S. The device described in claim 4, wherein the hammer shafts are supported by flexible reeds.

6. The device described in claim 4, wherein two magnetizable drums are rotated in opposite directions and wherein alternate hammer shafts operate in conjunction with one drum while the interspersed hammer shafts operate in conjunction with the other drum.

7. The device described in claim 6, wherein the hammer shafts are supported by flexible reeds, the reeds for successive hammer shafts alternating in their direction of mounting.

8. The device described in claim 4, wherein the electromagnetic means are coils, through which these hammer shafts extend.

9. The device described in claim 8, wherein the coils are rigidly mounted, and at least a portion of the hammer shafts constitute the magnetizable element, which shafts are movable within the rigidly-mounted coils.

10. The device described in claim 8, wherein the coils are mounted on the magnetizable elements for movement with the elements.

11. The device described in claim 4 wherein the drum is fiuted between the locations of the hammer shafts.

12. A hysteresis hammer drive comprising, in combination:

a print hammer mounted .for movement in a fixed path;

a first rotating magnetizable driving element;

selectively magnetizable driven means affixed to said hammer and positioned adjacent said rotating element;

means for generating a first fixed magnetic field in a circuit including said rotating element, said first fixed field passing through'said rotating element in a direction substantially parallel with said fixed path; and

means for energizing said driven means to produce a first auxiliary magnetic field substantially unidirectional with respect to said first fixed field, whereby a portion of said first fixed field is diverted through said driven means and a portion of said first auxiliary field is diverted through said circuit causing a hysteresis drag force to be imposed on said driven means, actuating said hammer in a first direction.

13. The hammer drive set forth in claim 12, further comprising:

a second rotating magnetizable driving element adjacent said driven means and mounted to move past said driven means in a direction opposite said first direction; and

means for generating a second fixed magnetic field in a circuit including said second rotating element, said second field passing through said second rotating element in a direction substantially parallel with but directionally opposed to said first fixed field, whereby energization of said driven means to produce a second auxiliary field opposite to said first auxiliary field causes a hysteresis drag force to be imposed on direction.

5 6 said driven means in a direction opposite to said rst 2,183,404 12/ 1939 Morrill 310-103 X 2,790,095 4/ 1957 Peck et a1 310-103 References Cited 3,172,352 3/ 1965 Helms 101-93 UNITED STATES PATENTS Dirks. 5 WILLIAM B. PENN, Primary Examiner Goin.

Laithwaite 335--229 Bradshaw.

Grottrup.

U.S. C1. X.R. 

